DMFs

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steelcityuk
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DMFs

Post by steelcityuk »

Hi All,

Whilst reading Car Mechanics magazine I came across a short piece in the 'trader column' about the problems of fitting solid flywheels to engines that were originally supplied with DMFs. According the the piece there's whispers of sheared cranks and the impending court action by a manufacturer.

Anyone heard anymore on this?

Steve.
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Re: DMFs

Post by Citroenmad »

I too have read that, its in a car mechanics from a few months ago?

There is a thread on here which someone who works for GSF or similar confirmed the problem. It seems cars with DMFs have some parts made from inferior/lighter materials and so could fail if a solid flywheel is fitted due to the DMF normally taking out more vibrations than a standard clutch.

Our 2.0HDi 8v 110 C5 has had a solid flywheel for 80K miles, 20K miles longer than its original DMF lasted. Though this engine was designed without a DMF originally (for the Xantia etc) and so it might explain why it does well on them.

I have known about this potential problem for a while and would not replace a DMF with a solid flywheel on anything else other than the earlier 2.0HDi 8vs. When the one on my 2.0HDi 16v went I didn't bother looking for a solid replacement (though I dont think there is one) as I didn't want to risk the possible effects. Despite being quite dissapointed that its DMF lasted only 29K miles :shock:
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Post by addo »

steelcityuk wrote:According the the piece there's whispers of sheared cranks and the impending court action by a manufacturer.

Anyone heard anymore on this?
Not I, although it seems fair to comment that contemporary design "ability" (in terms of stress analysis) enables parts to be designed that work well within design limits and a modest (smaller than once) factor of safety for operation beyond these limits.

A DMF replacement with solid, is quite likely to transform a cyclical stress event into one that's well outside design limits.

Low mileage DMF failures should be a trigger for class action against OEM designers, not a leg-up for aftermarket suppliers of a "bodge". Imagine if they had to recall every motor and replace it with a new one having inbuilt balance shaft! :shock:
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Re: DMFs

Post by waynedance »

If mine went I would replace with the same spec and not go solid conversion, buts that's me.
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Re: DMFs

Post by CitroJim »

waynedance wrote:If mine went I would replace with the same spec and not go solid conversion, buts that's me.
Yep, I'd be wary. Same for a DM crank pulley. It's there for a reason; as a harmonic damper. Replacing with a solid one could be a bad move...
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Re: DMFs

Post by wheeler »

Ford parts departmenst offer a genuine part solid conversion kit for the transit, i bet they have sold plenty of them aswell. This could be bad for ford if this is proven.
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Post by addo »

What if it were only specified for vehicles outside the statutory warranty period? Would that get them off the hook?
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Re: DMFs

Post by Citroenmad »

wheeler wrote:Ford parts departmenst offer a genuine part solid conversion kit for the transit, i bet they have sold plenty of them aswell. This could be bad for ford if this is proven.
I believe its a huge problem on Transits, apparently when the DMF fails it slips around covering the retaining bolts. The flywheel is often cut off after that :shock:

I can see why a solid flywheel would be an advantage on those and perhaps they run fine without them. I doubt a damaged crank will effect every model of engine/car as they might not be built down to such fine tolerances to allow them to give under extra vibration.

Has anyone got any information on why DMFs fail?

I have heard that an iffy starter motor can distroy them and have heard of cases where the DMF has been replaced only for it to fail shortly afterwards due to the starter.

I have also heard that making the engine labour, and so creating more vibrations, can wear out the DMF.

I suspect the biggest issue would be through heat and the pressure put on the flywheel when 'clutch control' is used to steady the car on any gradient.
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Re: DMFs

Post by lexi »

Was not the main purpose of DMF to cushion the now massive torque going from newer engines to gearbox?
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Re: DMFs

Post by SaabC5 »

I've seen cars with solid DMF conversions come in with sheared drive shaft splines, if you drive them hard this can happen. If you are mechanically sympathetic and don't dump the clutch you can get away with it for a considerble period of time.
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Re: DMFs

Post by robert_e_smart »

Yet more reasons to get an automatic.
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Re: DMFs

Post by steelcityuk »

Stop it Robert, it's bad enough as it is! All them pedals for a start...
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Re: DMFs

Post by Xaccers »

robert_e_smart wrote:Yet more reasons to get an automatic.
Automatics are far too complicated, I suspect that's the reason for Americans' apparent dopeyness, too much brain power used to drive automatics.
Give me a nice simple manual any day ;)
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Re: DMFs

Post by robert_e_smart »

:lol: :lol: :lol:

I have been trying to encourage my folks to get an Automatic C5 when their manual car expires. They have have had it from new, and DMF was replaced at 75K miles.

I suspect the new 6 speed autos to fare ok. They buy new, and drive them until they are done, so with regular oil changes, the autobox should in theory be a fairly safe bet.

Convincing my folks to get an auto, thats the hard bit!
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Re: DMFs

Post by Chris570 »

Xac wrote:
robert_e_smart wrote:Yet more reasons to get an automatic.
Automatics are far too complicated, I suspect that's the reason for Americans' apparent dopeyness, too much brain power used to drive automatics.
Give me a nice simple manual any day ;)
Have to say having been inside both an auto and a manual box an auto is far simpler and mated to the right engine an auto is simply the best.

now on a TCT or TD it simply has to be a manual. you have to have the control (and a TD with an auto would be painfully slow)
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